package org.g4studio.core.net.tftp;

import java.net.DatagramPacket;
import java.net.InetAddress;

/***
 * A final class derived from TFTPPacket definiing the TFTP Acknowledgement
 * packet type.
 * <p>
 * Details regarding the TFTP protocol and the format of TFTP packets can be
 * found in RFC 783. But the point of these classes is to keep you from having
 * to worry about the internals. Additionally, only very few people should have
 * to care about any of the TFTPPacket classes or derived classes. Almost all
 * users should only be concerned with the
 * {@link org.apache.commons.net.tftp.TFTPClient} class
 * {@link org.apache.commons.net.tftp.TFTPClient#receiveFile receiveFile()} and
 * {@link org.apache.commons.net.tftp.TFTPClient#sendFile sendFile()} methods.
 * <p>
 * <p>
 * 
 * @author Daniel F. Savarese
 * @see TFTPPacket
 * @see TFTPPacketException
 * @see TFTP
 ***/

public final class TFTPAckPacket extends TFTPPacket {
	/*** The block number being acknowledged by the packet. ***/
	int _blockNumber;

	/***
	 * Creates an acknowledgment packet to be sent to a host at a given port
	 * acknowledging receipt of a block.
	 * <p>
	 * 
	 * @param destination
	 *            The host to which the packet is going to be sent.
	 * @param port
	 *            The port to which the packet is going to be sent.
	 * @param blockNumber
	 *            The block number being acknowledged.
	 ***/
	public TFTPAckPacket(InetAddress destination, int port, int blockNumber) {
		super(TFTPPacket.ACKNOWLEDGEMENT, destination, port);
		_blockNumber = blockNumber;
	}

	/***
	 * Creates an acknowledgement packet based from a received datagram. Assumes
	 * the datagram is at least length 4, else an ArrayIndexOutOfBoundsException
	 * may be thrown.
	 * <p>
	 * 
	 * @param datagram
	 *            The datagram containing the received acknowledgement.
	 * @throws TFTPPacketException
	 *             If the datagram isn't a valid TFTP acknowledgement packet.
	 ***/
	TFTPAckPacket(DatagramPacket datagram) throws TFTPPacketException {
		super(TFTPPacket.ACKNOWLEDGEMENT, datagram.getAddress(), datagram.getPort());
		byte[] data;

		data = datagram.getData();

		if (getType() != data[1])
			throw new TFTPPacketException("TFTP operator code does not match type.");

		_blockNumber = (((data[2] & 0xff) << 8) | (data[3] & 0xff));
	}

	/***
	 * This is a method only available within the package for implementing
	 * efficient datagram transport by elminating buffering. It takes a datagram
	 * as an argument, and a byte buffer in which to store the raw datagram
	 * data. Inside the method, the data is set as the datagram's data and the
	 * datagram returned.
	 * <p>
	 * 
	 * @param datagram
	 *            The datagram to create.
	 * @param data
	 *            The buffer to store the packet and to use in the datagram.
	 * @return The datagram argument.
	 ***/
	DatagramPacket _newDatagram(DatagramPacket datagram, byte[] data) {
		data[0] = 0;
		data[1] = (byte) _type;
		data[2] = (byte) ((_blockNumber & 0xffff) >> 8);
		data[3] = (byte) (_blockNumber & 0xff);

		datagram.setAddress(_address);
		datagram.setPort(_port);
		datagram.setData(data);
		datagram.setLength(4);

		return datagram;
	}

	/***
	 * Creates a UDP datagram containing all the TFTP acknowledgement packet
	 * data in the proper format. This is a method exposed to the programmer in
	 * case he wants to implement his own TFTP client instead of using the
	 * {@link org.apache.commons.net.tftp.TFTPClient} class. Under normal
	 * circumstances, you should not have a need to call this method.
	 * <p>
	 * 
	 * @return A UDP datagram containing the TFTP acknowledgement packet.
	 ***/
	public DatagramPacket newDatagram() {
		byte[] data;

		data = new byte[4];
		data[0] = 0;
		data[1] = (byte) _type;
		data[2] = (byte) ((_blockNumber & 0xffff) >> 8);
		data[3] = (byte) (_blockNumber & 0xff);

		return new DatagramPacket(data, data.length, _address, _port);
	}

	/***
	 * Returns the block number of the acknowledgement.
	 * <p>
	 * 
	 * @return The block number of the acknowledgement.
	 ***/
	public int getBlockNumber() {
		return _blockNumber;
	}

	/*** Sets the block number of the acknowledgement. ***/
	public void setBlockNumber(int blockNumber) {
		_blockNumber = blockNumber;
	}
}
